The mixer, being a basic block of IC for communication, converts a signal frequency of one band into that of another band. Particularly, in the IC for communication, a low supply power and a low power dissipation are very important because it must operate for a long period of time using a small power supply such as a battery. However, even when the supply power and the power dissipation are low, a high degree of linearity is also required.
The present invention belongs to a technical field which implements a high speed mixer applicable to an IC for communication into an integrated circuit block. In a prior art, it is a general trend to implement a high speed mixer using BJT or MESFET that has large transconductance. However, as the process technology of integrated circuit advances, there has been an increasing need for implementing this kind of mixer using a MOS transistor that is most suitable to the integration density. However, in case of the MOS device, if a conventional technique is used, it is difficult to achieve both high speed operation and small power dissipation. Nevertheless, because the mixer composed of a device with small transconductance, such as a MOS device, operating at a high frequency dissipates large power, an additional part is required to achieve low output impedance. As discussed above, in a prior art, a lot of electrical power must be dissipated in order for the CMOS mixer operating at high speed to have a low output impedance. As a result, there has been a need for implementing the operation of the mixer at low voltage and power that is effective even when using a low speed device, such as CMOS.